This invention relates to ceramic tile burners of the type which are used in natural gas combustion systems as flame holders and flame spreaders.
Due to the increasing demand on manufacturers to make the most efficient use of space, it is often desirable to reduce the size of equipment. With gas-fired equipment using ceramic tile burners, use of ceramic tile burners with smaller surface areas can help in decreasing overall size of the equipment.
Ceramic tile burners are operated at a variety of specific heat release rates (surface heat loadings). At low surface heat loads, ceramic tiles act as radiant burners. Combustion of gaseous reactants passing through channels or pores of the ceramic tile takes place within the ceramic tile, and the tile becomes radiant. Ignition of the incoming reactants is caused by the high temperature of the ceramic and a flame holding capability is not needed.
At moderate surface heat loading rates, combustion takes place at or above the ceramic tile and the tile is cooled by the incoming reactants. In this regime, known as "blue flame" operation, the ceramic tile acts as a distributor, thermal barrier, and flame holder. Segments between the pores of the tiles cause turbulent recirculation zones to form, and this recirculation of hot gases ignites the combustion reactants as they exit the tile, keeping the flame stable. The ceramic tile. which is cooled by the reactants, effectively insulates the upstream reactants from the hot downstream combustion products, preventing flashback.
Increasing the surface heat loading capability of a ceramic tile burner to high levels, as required to maintain the same heat output while decreasing tile surface area, produces very high velocity reactant flow when low porosity tiles are used. This causes an unstable flame and noisy combustion. The unstable combustion also contributes to unacceptable high carbon monoxide levels. Experimentally, this phenomenon has been found to occur with low porosity (approximately 30% open) ceramic tiles at surface heat loading rates above about 3000 BTU/hr in.sup.2. With high porosity ceramic tiles, channel wall thicknesses are small. This has a detrimental effect on the formation of downstream recirculation zones. For this reason, the flame holding capabilities of the tiles are poor, resulting in unstable combustion.
Accordingly, it is an object of the present invention to provide a ceramic tile burner that is capable of withstanding higher surface heat loadings than can known ceramic tile burners.
It is another object of the present invention to provide a ceramic tile burner that delivers the same heat transfer capacity as known ceramic tile burners while having a considerably smaller surface area.
It is yet another object of the present invention to provide a ceramic tile burner that can utilize a ceramic body of much higher porosity that can be used at high surface heat loadings by known ceramic tile burners while retaining flame stability and acceptable carbon monoxide levels.
It is still another object of the present invention to provide a high porosity ceramic tile burner which in spite of having extremely thin channel walls, still has adequate recirculation zones and flame holding capabilities.